1. Field of the Invention
This invention relates generally to video signal encoding systems. More particularly, the present invention is concerned with a digital encoding system for encoding video signals which uses bi-orthogonal wavelet coding to compress digitized video data.
2. Description of the Prior Art
There is currently a need for the reliable transmission and reception of real time television video and/or television sub video over a narrow bandwidth. For example, in the transmission of telemetry video data from a missile the telemetry channel may have a bandwidth of two megahertz or even substantially less than two megahertz.
Prior art methods and apparatus for compressing real time video data include Adaptive Differential Pulse Code modulation (ADPCM), Joint Photography Experts Group (JPEG) and Motion Picture Experts Group (MPEG). These methods of encoding real time video data are generally not capable of sufficient bandwidth reduction or are susceptible to excessive data loss in a noisy environment.
For example, Adaptive Differential Pulse Code modulation, which is used by the International Range Instrumentation Group to transmit telemetry data, is noise immune, however, it is not capable of real time video data compression to allow accurate and reliable transmission of the data over a channel narrower than five megahertz. Even moderately complex video images overload an ADPCM encoder causing it to lose fields and even multiple frames of video data.
Both Joint Photography Experts Group and Motion Picture Experts Group methods and encoders are capable of compressing real time video data sufficiently to allow the data to be transmitted over a two megahertz channel, however, these methods and encoders are susceptible to noise. A single noise hit, for example, can cause the lose of an entire video field or even multiple fields. In addition, JPEG and MPEG encoding can distort an image with the random appearance of square blocks caused in a noisy environment by a reflection of eight by eight pixel discrete cosine transform used encode the video data.
Accordingly, there is a need for an encoder to accurately and reliably encode complex video data which allow for its transmission over a bandwidth of two megahertz without distortion of the data caused by noise.